Vehicle engines generally comprise certain accessories that are used in the operation of the engine and vehicle. Such accessories can include a power steering pump, an air conditioning compressor, an alternator, an oil pump, a fuel pump and so on. These accessories are generally driven by a serpentine belt. The serpentine belt engages a pulley on each accessory as well as on an engine crankshaft. The engine crankshaft provides the torque to drive the accessories.
As the belt is driven by the crankshaft it is necessarily subject to engine speed variations during acceleration and deceleration of the vehicle. In other words the operating speed of the accessories is directly proportional to the speed of the engine. The variations in engine speed result in inefficient operation of the accessories because each accessory must be designed to operate satisfactorily over the entire engine speed range. This necessarily means that the efficiency is less than optimum for most of the speed range. Therefore it is desirable to decouple the accessories from the crankshaft so they can be driven at a constant, optimum speed.
Representative of the art is U.S. Pat. No. 4,969,857 to Kumm (1990) which discloses a variable speed accessory drive having a flat belt driving a variable diameter pulley wherein a fixed diameter pulley attached to the variable diameter pulley is used to drive another belt coupled to the accessories.
Also representative of the art is U.S. Pat. No. 4,305,488 to McIntosh (1981) which discloses a vehicle accessory drive assembly that incorporates a speed-increasing planetary gear set with an engine driven carrier input.
Kumm represents a particularly complex response to the problem, requiring many component parts in the CVT pulley which must operate in concert to perform properly. Further, Kumm will not operate with a multiple-ribbed belt which is the predominant driver in accessory drives.
A simple planetary ball continuously variable transmission is desirable to reduce possible failure modes for an accessory drive system as well as to increase durability.
Representative of the art is U.S. Pat. No. 6,461,268 B1 to Milner (2002) which discloses a continuously variable transmission of the type having planetary members in rolling contact with radially inner and outer races each comprising two axially spaced parts with control means for selectively varying the axial separation of the two parts of one race.
What is needed is a constant speed accessory drive that drives belt driven accessories at a substantially constant speed while using an infinitely variable speed ratio planetary ball transmission having a self locking drive. The present invention meets this need.